ADO.NET2.0增加了一些新的特性，其中就包括异步查询。这个特点在需要执行多个查询的时候，或者查询过程比较常的时候就很有用。而默认情况下是不开启异步查询的，必须要在连接字符串中显示的打开，如下图，图中划线的就是需要显示制定的，后面一个是显示的打开MARS。
下面的代码包括了异步查询的三种方法，所以代码都可以测试运行，数据库是NorthWind.
其中一个运行页面如图：
首先是页面源码：
后台代码：
public string ConStr = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
BindData();
//BindMultiData();
//BindMultiDataArray();
//BindDataWithCallBack();
}
}
//异步查询的poll方式，最普通的方式
private void BindData()
{
string QueryStr = "SELECT * FROM customers";
using (SqlConnection Con = new SqlConnection(ConStr))
{
SqlCommand Cmd = new SqlCommand(QueryStr, Con);
IAsyncResult ASynResult;
SqlDataReader Da;
try
{
Con.Open();
//begin方法返回一个IAsyncResult对象，用来检查执行是否完成
ASynResult = Cmd.BeginExecuteReader(CommandBehavior.CloseConnection);
while (!ASynResult.IsCompleted)
{
Response.Write("异步查询</br>");
ASynResult.AsyncWaitHandle.WaitOne(3000, true);
//System.Threading.Thread.Sleep(10);
}
Da = Cmd.EndExecuteReader(ASynResult);
GridView1.DataSource = Da;
GridView1.DataBind();
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
}
}
//异步查询的wait方式，使用多个等待句柄来异步查询，必须等待所有进程完成处理结果集
private void BindMultiData()
{
string CusQueryStr = "SELECT * FROM customers WHERE CompanyName = 'Alfreds Futterkiste'";
string SupQueryStr = "SELECT Customers.CompanyName, Customers.ContactName, " +
"Orders.OrderID, Orders.OrderDate, " +
"Orders.RequiredDate, Orders.ShippedDate " +
"FROM Orders, Customers " +
"WHERE Orders.CustomerID = Customers.CustomerID " +
"AND Customers.CompanyName = 'Alfreds Futterkiste' " +
"ORDER BY Customers.CompanyName, Customers.ContactName";
using (SqlConnection MyCon = new SqlConnection(ConStr))
{
SqlCommand CusCmd = new SqlCommand(CusQueryStr, MyCon);
SqlCommand SupCmd = new SqlCommand(SupQueryStr, MyCon);
SqlDataReader CusDr;
SqlDataReader SupDr;
IAsyncResult CusIsynResult;
IAsyncResult SupIsynResult;
//创建句柄数组
System.Threading.WaitHandle[] WHandles = new System.Threading.WaitHandle[2];
System.Threading.WaitHandle CusHandle;
System.Threading.WaitHandle SupHandle;
MyCon.Open();
CusIsynResult = CusCmd.BeginExecuteReader(CommandBehavior.CloseConnection);
SupIsynResult = SupCmd.BeginExecuteReader(CommandBehavior.CloseConnection);
CusHandle = CusIsynResult.AsyncWaitHandle;
SupHandle = SupIsynResult.AsyncWaitHandle;
//将等待句柄赋给句柄数组
WHandles[0] = CusHandle;
WHandles[1] = SupHandle;
//将数组传给waitall方法，等待所以的异步查询完成
System.Threading.WaitHandle.WaitAll(WHandles);
CusDr = CusCmd.EndExecuteReader(CusIsynResult);
SupDr = SupCmd.EndExecuteReader(SupIsynResult);
GridView1.DataSource = CusDr;
GridView1.DataBind();
GridView2.DataSource = SupDr;
GridView2.DataBind();
MyCon.Dispose();
CusCmd.Dispose();
SupCmd.Dispose();
}
}
//采用WaitAny方式，优点是不用等待所有进程都完成才处理结果集
private void BindMultiDataArray()
{
string CusQueryStr = "SELECT * FROM customers WHERE CompanyName = 'Alfreds Futterkiste'";
string SupQueryStr = "SELECT Customers.CompanyName, Customers.ContactName, " +
"Orders.OrderID, Orders.OrderDate, " +
"Orders.RequiredDate, Orders.ShippedDate " +
"FROM Orders, Customers " +
"WHERE Orders.CustomerID = Customers.CustomerID " +
"AND Customers.CompanyName = 'Alfreds Futterkiste' " +
"ORDER BY Customers.CompanyName, Customers.ContactName";
using (SqlConnection MyCon = new SqlConnection(ConStr))
{
SqlCommand CusCmd = new SqlCommand(CusQueryStr, MyCon);
SqlCommand SupCmd = new SqlCommand(SupQueryStr, MyCon);
SqlDataReader CusDr;
SqlDataReader SupDr;
IAsyncResult CusIsynResult;
IAsyncResult SupIsynResult;
System.Threading.WaitHandle[] WHandles = new System.Threading.WaitHandle[2];
System.Threading.WaitHandle CusHandle;
System.Threading.WaitHandle SupHandle;
int WHindex;
MyCon.Open();
CusIsynResult = CusCmd.BeginExecuteReader(CommandBehavior.CloseConnection);
SupIsynResult = SupCmd.BeginExecuteReader(CommandBehavior.CloseConnection);
CusHandle = CusIsynResult.AsyncWaitHandle;
SupHandle = SupIsynResult.AsyncWaitHandle;
WHandles[0] = CusHandle;
WHandles[1] = SupHandle;
for (int i = 0; i < WHandles.Length; i++)
{
//waitany好处在于不必等待所有异步操作完成
WHindex = System.Threading.WaitHandle.WaitAny(WHandles);
switch (WHindex)
{
case 0:
CusDr = CusCmd.EndExecuteReader(CusIsynResult);
GridView1.DataSource = CusDr;
GridView1.DataBind();
break;
case 1:
SupDr = SupCmd.EndExecuteReader(SupIsynResult);
GridView2.DataSource = SupDr;
GridView2.DataBind();
break;
}
}
MyCon.Dispose();
CusCmd.Dispose();
SupCmd.Dispose();
}
}
//通过回调来实现异步查询
private void BindDataWithCallBack()
{
string SupQueryStr = "SELECT Customers.CompanyName, Customers.ContactName, " +
"Orders.OrderID, Orders.OrderDate, " +
"Orders.RequiredDate, Orders.ShippedDate " +
"FROM Orders, Customers " +
"WHERE Orders.CustomerID = Customers.CustomerID " +
"AND Customers.CompanyName = 'Alfreds Futterkiste' " +
"ORDER BY Customers.CompanyName, Customers.ContactName";
using (SqlConnection MyCon = new SqlConnection(ConStr))
{
SqlCommand SupCmd = new SqlCommand(SupQueryStr, MyCon);
SqlDataReader SupDr;
IAsyncResult SupIsynResult;
MyCon.Open();
AsyncCallback Callback = new AsyncCallback(CallBackMethod);
SupIsynResult = SupCmd.BeginExecuteReader(Callback, SupCmd,CommandBehavior.CloseConnection);
System.Threading.Thread.Sleep(100);
MyCon.Dispose();
SupCmd.Dispose();
}
}
//回调方法
public void CallBackMethod(IAsyncResult IResult)
{
SqlCommand Command = (SqlCommand)IResult.AsyncState;
SqlDataReader dr = Command.EndExecuteReader(IResult);
GridView1.DataSource = dr;
GridView1.DataBind();
}
}
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